Designed to mimic the compact profile and light weight of Clan-tech XL Engines, the Light Fusion Engine weighs only 75% of a standard Fusion Engine. While not as dramatic as the 50% weight saving of an XL Engine, the real benefit of the Light Fusion Engine is that while it intrudes into the side torsos of a BattleMech, it takes up the same amount of space as a Clan extra-light engine, allowing a Light Fusion Engine equipped 'Mech to survive the destruction of a side-torso that would cripple an Inner Sphere XL engine equipped 'Mech.

While introduced by the Lyran Alliance in 3062, the technology actually stems from the Wolf's Dragoons and Blackwell Corporation. With dwindling supplies of Clan-Tech XL Engines, after the initial Clan Invasion the Dragoons charged Blackwell with developing a new form of lighter than standard engine yet with the same bulk as the Clan extralight.

Using the Lostech protective energy damping grid of the Steiner Stadium on Solaris VII as a base, Blackwell engineers were able to reduce the level of physical shielding with the energy field assisting in keeping the engine's fusion reaction in check. As rumors of this technology began to leak out in 3053, Archon-PrinceVictor Steiner-Davion of the Federated Commonwealth entered into protracted and ultimately fruitless negotiations with Blackwell, becoming apparent either the rumors were false or Blackwell would not sell the technology to anybody outside of the Dragoons.

In 3058, after the formation of the Lyran Alliance, the Lyran Intelligence Corps discovered that while a long way from full mass-production, Blackwell had succeeded in developing a prototype. Recognizing the awesome potential of the technology and viewing the possibly alienation of the Dragoons as worth the cost to secure it for the Alliance, ArchonKatherine Steiner-Davion authorized Loki to steal the prototype. It took Defiance Industries four years and unlimited funding and resources, but the Lyran Alliance Armed Forces were duly impressed with the resulting light fusion engine. [1]